This invention is directed to a radial flow electron gun of elongated large area design.
R. C. Knechtli U.S. Pat. No. 3,831,052 describes a hollow cathode gas discharge device which can be designed with considerable length to achieve electron discharge in a large area, along a fairly long window. It can be employed wherever a high density beam of electrons is required, such as in exciting a laser or for the curing of paint, and like uses. The background also includes an article entitled "The Design of Large Area Electron Beam Guns" published at the Electron and Ion Beam Science and Technology Conference on May 12-17, 1974 by Kurt Amboss. This is a background article discussing a variety of electron design solutions with their relative attractiveness depending upon the constraints imposed by the foil window, type of cathode, voltage breakdown, uniform current density, and current uniformity during modulation. A number of solutions are suggested, particularly relating the various limitations. However, the problem and solution of accelerating field perturbation on electron flow in the anode drift region is not disclosed.
Whenever uniform electron delivery or exposure is required, particular attention must be paid to the electron optical design to produce a beam of large area which is capable of retaining a highly uniform current density distribution over a wide range of operating currents.